Device for measuring at least one parameter of a flowing medium

ABSTRACT

A device for measuring at least one parameter, in particular of a volumetric flow, of a medium flowing in a line, in particular of the intake air volumetric flow of an internal combustion engine, includes at least one measuring element around which the medium flows. Constrictions, which do not uniformly constrict the cross-section of the line, do not produce any ring-shaped eddies that may be heard in the form of whistling noises.

FIELD OF THE INVENTION

The present invention relates to a device for measuring at least oneparameter of a medium flowing in a line.

BACKGROUND INFORMATION

German Published Patent Application No. 196 52 153 describes a devicehaving a measuring element for measuring a mass of a flowing medium, inwhich a flow straightener with a screen is provided upstream from themeasuring element. The flow straightener with screen is installed in arigid conduit inside the line, thereby constricting the line.

German Published Patent Application No. 197 38 337 and U.S. Pat. No.5,892,146 respectively describe a hot-wire air-flow meter, having anorifice that forms a single unit with one wall of the line and islocated upstream from the measuring element. This arrangement constrictsthe line and increases the flow velocity of a forward mass flow withpulsating flow downstream from, and within the diameter of, the orificewithout destroying the flow.

Ring-shaped constrictions in devices, such as those described above may,under certain flow conditions, produce acoustic disturbances in the linethat become noticeable in the form of whistling sounds.

These disturbances are triggered by ring-shaped eddies arisingdownstream behind one edge of the constriction and propagate in thedirection of flow of the line.

German Published Patent Application No. 198 156 58 describes a devicehaving a measuring element to measure a mass of a medium flowing in aline, with a flow pipe being located in the line and the measuringelement being provided in the flow pipe. Any loud, disturbing whistlingnoises that occur are reduced by structural grooves in the end face ofthe flow pipe.

SUMMARY

The device according to the present invention has the advantage thatacoustic disturbances are avoided. This result is achieved in thatsuppression elements are used to reduce the formation of ring-shapededdies.

At least one prevention element may be integrated into a rigid conduitof a flow straightener or into a second rigid conduit to simplifymanufacturing.

If there is no flow straightener or rigid conduit, integrating at leastone prevention element into one wall of a line may simplifymanufacturing.

According to one arrangement of the suppression elements, the latter maybe evenly distributed in the circumferential direction of the line andhave the same shape to avoid distorting the velocity profile of theflow.

At least one suppression element may be configured as an elevation inthe line to simplify manufacturing.

One example embodiment of the suppression element provides an orificewith different sections, the radial spacing of which varies in relationto a center line of the line.

The prevention elements may be rounded against the main direction offlow to avoid distorting the velocity profile of the flow.

A tubular body may be provided in the line, thereby avoiding a deviationin the measurement characteristic of a measuring element, caused by theimpact of fluid or solid particles.

A protective screen may be integrated into the line or into the tubularbody.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a device according to the presentinvention having a flow straightener and a screen, in which at least oneprevention element according to the present invention is provided.

FIGS. 2a and 2 b illustrate a section of the device illustrated in FIG.1.

FIGS. 3a to 3 d illustrate several example embodiments of suppressionelements.

FIG. 4 is a perspective view of a device according to the presentinvention with a tubular body.

DETAILED DESCRIPTION

FIG. 1 is a partial cross-sectional view of a device 1 for measuring atleast one parameter of a medium flowing in a line 14, in particular aparameter of the intake air mass of an internal combustion engine.Parameters of a flowing medium are, for example, volumetric flow fordetermining a mass, a temperature, a pressure or a flow velocity, whichare detected using suitable sensors. Device 1 may also be used tomeasure additional parameters.

The flowing medium may be air, a gas mixture or a fluid. The internalcombustion engine may be, for example, a mixture-compressing engine withexternally-supplied ignition or even an air-compressing engine withspontaneous ignition.

Device 1 includes at least one measuring unit 4, which, for example, maybe plugged into an instrument gland 7 of device 1, and in which isprovided a measuring element 25. Measuring element 25 may be, forexample, a temperature sensor (such as that described in GermanPublished Patent Application No. 42 28 484), a pressure sensor (such asthat described in German Published Patent Application No. 34 35 794), oran air-flow sensor, which detects the corresponding parameters. Forexample, a volumetric air-flow sensor is selected as one of thedifferent possible sensors.

Measuring unit 4 includes, for example, a narrow, rod-like, cuboid shapethat extends longitudinally in the direction of a plug-in axis 10 andmay be introduced, for example, by plugging, into an opening provided inone wall 13 of instrument gland 7. Wall 13 includes an inner wall 15 andlimits a flow cross-section of line 14, which includes, for example, acircular cross-section, in the center of which a center axis 21 extendsparallel to wall 13 in direction 18 of the flowing medium and isoriented perpendicular to plug-in axis 10. In FIG. 1, the direction ofthe flowing medium is illustrated by arrows 18 and it moves from left toright.

Measuring element 25 is inserted into the flowing medium together withmeasuring unit 4. A measuring channel 27, in which measuring element 25is provided for measuring the medium flowing in instrument gland 7, isincorporated into measuring unit 4 of device 1. The structure of ameasuring unit 4 of this type, having a measuring element 25, isdescribed, for example, in German Published Patent Application No. 44 07209.

A screen 32 and a sleeve-like flow straightener 30, which is attached,for example, to a rigid conduit 33, are provided upstream from measuringelement 25. Rigid conduit 33 includes an inner diameter that is smallerthan line 14, thus forming a constriction 35.

Flow straightener 30 is made, for example, of plastic and is produced,for example, by injection molding and includes a multiplicity of, forexample, rectangular openings 34 oriented in the direction of flow.

The structure of a flow straightener 30 of this type, having screen 32,is described, for example, in German Published Patent Application No.196 52 753. At least one acoustic prevention element 40 is integrallyattached, for example, to rigid conduit 33 of flow straightener 30.

For the purpose of final assembly of device 1, the assembly unit formedby flow straightener 30 and screen 32 is inserted into a, for example,circular opening 47 provided at the upstream end of instrument gland 7,until ring-shaped wall 50 of flow straightener 30 comes into contactwith a stop 52 of instrument gland 7 that reduces the cross-section ofopening 47.

To permanently hold flow straightener 30 in place in opening 47, flowstraightener 30 includes barbed hook elements 57 on rigid conduit 33,which, for example, extend slightly outward radially from its externalsurface 55 and may correspondingly latch into place in a groove 60provided in an inner wall of opening 47 in instrument gland 7.

FIG. 2a illustrates an enlarged portion of FIG. 1, identified by adotted line. Locking hooks 63 are elastic and have locking heads 65 thatextend inwardly in a radial direction. When screen 32 is installed,locking heads 65 grip around an edge of screen 32 like pliers and restagainst a surface 68 of screen 32 facing measuring unit 4, so thatlocking heads 65 press screen 32 against a circumferential shoulder 74of flow straightener 30 formed by inner surface 70.

A second rigid conduit 72 is located downstream behind rigid conduit 33.Second rigid conduit 72 is provided at the same radial distance fromcenter line 21 as inner surface 70. At the downstream end of secondrigid conduit 72 is provided at least one acoustic prevention element40, which, for example, forms a single unit and extends into line 14 ina radial direction. Second rigid conduit 72 is pressed against shoulder52, for example, by rigid conduit 33. However, it may also be fastenedin line 14, like rigid conduit 33. Acoustic suppression element 40 actsmechanically on the flow in line 14, thus preventing ring-shaped eddiesthat form downstream behind an edge of a constriction and propagate inthe direction of flow of the line, becoming noticeable in the form ofwhistling noises.

In a cross-sectional view along main direction of flow 18 throughprevention element 40, prevention element 40 includes, for example, arounded shape 41 in the upstream direction and a rough edge 42 in thedownstream direction. The at least one 5 suppression element 40constricts line 14 by 2% to 30%.

FIG. 2b illustrates the arrangement of second rigid conduit 72 and rigidconduit 33 as a single unit. Viewed in the downstream direction, rigidconduit 33 includes an extension arm 77 that continues behind screen 32along inner wall 15. Acoustic prevention element 40, which extends intoline 14 in a radial direction, is located at end 78 of extension arm 77.Screen 32 is installed, for example, by bending rigid conduit 33outwardly radially in the region of extension arm 77 and then insertingscreen 32.

FIGS. 3a to 3 d illustrate several example embodiments of preventionelement 40. The same reference numbers used in the previous figuresidentify the same or functionally equivalent components.

FIG. 3a illustrates a prevention element 40 that is configured as aradial elevation 79 relative to center line 21 and includes arectangular cross-section at right angles to main direction of flow 18.Elevations 79, for example, are of the same size and are evenlydistributed along a circumferential line 80 of line 14, which isindicated by the dotted line.

Radial elevations 79 illustrated in FIG. 3b have a semicircularcross-section at right angles to main direction of flow 18. FIG. 3cillustrates that radial elevations 79 may have different geometries inone embodiment of the device.

In the radial cross-section, they are, for example, trapezoidal orsemicircular. Elevations 70 are distributed evenly and arrangedsymmetrically.

FIG. 3d illustrates a prevention element 40 configured as an orifice 82,the radial limiting line 81 of which does not have a constant innerdiameter and is configured, for example, in the shape of a wave.

Prevention elements 40 in this case form, for example, a single unitwith instrument gland 7.

FIG. 4 illustrates device 1 in a line 14 within which a medium flows.The same reference numbers used in the previous figures identify thesame or functionally equivalent components. In line 14, and spaced at aradial distance from line 14, is provided, for example, a tubular body85, around which the medium flows and which serves as an element 84 forreducing the impact of fluid or solid particles on measuring element 25.

Prevention elements 40 are arranged in main direction of flow 18 so thattheir rough edges 42 are located after or at the same level as a tubularinlet opening 88 in tubular body 85 when viewed in the axial direction.

Prevention elements 40 in this case are connected to instrument gland 7,for example, forming a single unit. However, they may also be providedas additional units or only on tubular body 85.

Prevention elements 40 may, for example, also be provided in tubularbody 85.

The at least one prevention element 40, 79, 82 is connected, forexample, to tubular body 85, for example, forming a single unit. Tubularbody 85 includes a flow channel 87 and a protective screen 90, locatedin the region of its upstream end, as an element 84 for reducing theimpact of fluid or solid particles on measuring element 25.

Protective screen 90 may be configured, for example, as a wire mesh orplate-type screen. Any other shape is also possible. Plastic, metal,ceramic or glass may be used as the material for protective screen 90,in the case of both the wire mesh and plate-type protective screen 90.Plate-type protective screen 90 made of plastic may be produced, forexample, entirely by injection molding or by creating screen openings 94in a plate-type basic body using a material-removal method. Plate-typeprotective screen 90 made of metal may be produced, for example, from asheet by punching, eroding, drilling, etc.

A direction of flow 98 exists at a slight distance from protectivescreen 90 in the downstream region of flow channel 87. Direction of flow98 extends roughly parallel to main direction of flow 18. Line 14 has acenter line 21, which, for example, is also the center line of tubularbody 85. Measuring unit 4, for example, extends into tubular body 85. Aconnector end of measuring unit 4 that contains the electricalconnections, for example in the form of connector prongs, remains, forexample, outside line 14. Measuring element 25, which is in contact withthe air flowing through flow channel 87 and is used for detecting airmass entering the internal combustion engine, is provided in aconventional manner in measuring unit 4. Measuring element 25 may beconfigured in a conventional manner, for example, in the form of atleast one temperature-dependent resistor. In particular, it is possibleto configure measuring element 25 as a micromechanical component thathas a dielectric diaphragm on which resistor elements are provided, asdescribed, for example, in German Published Patent Application No. 43 38891 and U.S. Pat. No. 5,452,610, respectively. It is also conceivable toincorporate measuring element 25 into line 14 or tubular body 85 withouta measuring unit.

At least two braces 101, which hold tubular body 85 in place in line 14,are provided, for example, on tubular body 85. In addition to holdingtubular body 85 in place, braces 101 also increase the pressure drop inthe air flow between line 14 and tubular body 85, thus increasing theamount of air flowing through flow channel 87, and braces 101 alsostraighten the intake air flow in the desired manner.

Tubular body 85 may also be provided in line 14 without braces 101, forexample, it may be fastened to measuring unit 4.

Protective screen 90 includes, for example, bars 105 that are positionedperpendicular to each other, for example perpendicular to plug-in axis10 and horizontal to plug-in axis 10, with bars 105 positionedhorizontally relative to center line 21, for example, being arranged atan angle of approximately 30 degrees relative to plug-in axis 10. Thisvaries main direction of flow 18 downstream behind protective screen 90.Protective screen 90 may also be oriented at an angle in relation tomain direction of flow 18. Dirt particles and fluid droplets aredeposited on protective screen 90 and are directed to an inner wall 107of line 14 or of tubular body 85, thus moving past inlet opening 110 ofmeasuring unit 4 or past measuring element 25.

What is claimed is:
 1. A device for measuring at least one parameter ofa medium flowing in a main direction of flow in a line, comprising: ameasuring element circumflowed by the medium and positioned in the line;and at least one constriction configured to produce acousticdisturbances in the medium and positioned along a circumferential lineof the line upstream of the measuring element; wherein the at least oneconstriction is circumflowed by the medium and includes amechanical-acoustic prevention element, the prevention element includingat least two radial elevations circumflowed by the medium and the atleast two radial elevations being arranged along the circumferentialline, so as to at least reduce the acoustic disturbances.
 2. The deviceaccording to claim 1, wherein the at least one parameter includes a massflow.
 3. The device according to claim 2, wherein the mass flow includesan intake air mass flow of an internal combustion engine.
 4. The deviceaccording to claim 1, further comprising at least one element positionedin the line and configured to reduce an impact of one of fluid and solidparticles on the measuring element.
 5. The device according to claim 4,wherein the element configured to reduce the impact of one of fluid andsolid particles includes a tubular body having a flow channel throughwhich the medium flows, the measuring element being located in thetubular body.
 6. The device according to claim 4, wherein the elementconfigured to reduce the impact of one of fluid and solid particlesincludes a protective screen located in one of the line and the tubularbody.
 7. The device according to claim 1, wherein the radial elevationincludes a rectangular cross-section arranged at a right angle to themain direction of flow.
 8. The device according to claim 1, wherein theradial elevation includes a trapezoidal cross-section arranged at aright angle to the main direction of flow.
 9. The device according toclaim 1, wherein the radial elevation includes one of an oval and acircular cross-section arranged at a right angle to the main directionof flow.
 10. The device according to claim 1, wherein radial elevationsare evenly spaced in relation to one another along a radialcircumferential line of the line.
 11. The device according to claim 1,wherein radial elevations have a same shape.
 12. The device accordingclaim 1, wherein the line includes a center line, the acousticprevention element including an aperture provided in the line and havinga radial limiting line, a radial distance between the radial limitingline and the center line varying in a radial circumferential direction.13. The device according to claim 12, wherein the radial limiting lineof the aperture is wave-shaped.
 14. The device according to claim 1,wherein the at least one prevention element is rounded against the maindirection of flow.
 15. The device according to claim 1, furthercomprising a flow straightener provided in the line and integrated intoa rigid conduit that is insertable into the line, the at least oneprevention element provided as a single unit on the rigid conduit. 16.The device according to claim 1, wherein the at least one preventionelement is provided as a single unit on a rigid conduit that isinsertable into the line.
 17. The device according to claim 1, whereinthe at least one prevention element is configured as a single unit witha wall of the line.
 18. The device according to claim 1, wherein theconstriction is configured to at least reduce the ring-shaped eddies.19. The device according to claim 18, wherein the constriction at leastreduces the acoustic disturbance associated with the ring-shaped eddies.